Neuro-ventilatory efficiency and extubation readiness in critically ill patients
Critical Care, 08/09/2012
Liu L et al. – This study shows that a mixed group of critically ill patients who fail weaning have increased neural respiratory drive and impaired ability to convert neuromuscular activity into tidal ventilation, in part due to diaphragm weakness.Methods
- Airway pressure, flow, and volume, breathing frequency and diaphragm electrical activity were measured in a heterogeneous group of patients deemed ready for a spontaneous breathing trial.
- Efficiency to convert neuromuscular activity into inspiratory pressure was calculated as the ratio of negative airway pressure and diaphragm electrical activity during an inspiratory occlusion.
- Efficiency to convert neuromuscular activity into volume was calculated as the ratio of the tidal volume and diaphragm electrical activity.
- All variables were obtained during a 30 minute spontaneous breathing trial on CPAP of 5cm H2O and compared between patients who succeeded extubation to those who either failed the spontaneous breathing trial or those who passed, but then failed extubation.
- Out of 52 patients enrolled in the study, 35 (67.3%) were successfully extubated and 17 (32.7%) failed.
- Patients who failed had higher diaphragm electrical activity (48%; P<0.001), and a lower efficiency to convert neuromuscular activity into inspiratory pressure and tidal volume (40% (P<0.001) and 53% (P<0.001), respectively.
- Neuroventilatory efficiency demonstrated the greatest predictability for weaning success.